The present invention relates generally to a system and method by which an enclosure can be heated and passively cooled by absorbing heat from the sun and releasing excess heat into the atmosphere.
Most enclosures such as homes, offices, and shops intended for human habitation require heating and cooling methods which are rather exact and always adjustable. However, there are several types of enclosures which require a less exact method of heating and cooling, and even enclosures intended for human habitation do not always require exact temperature control. Some examples of enclosures which need to be protected from extreme temperature changes, but not maintained at a constant humanly habitable temperature at all times are livestock and poultry shelters, and remote electrical installations. Despite the ease with which a home or business can, in most cases, be heated for a reasonable amount of money, there are few financially feasible methods by which a remote enclosure can be heated and cooled by equivalent apparatus when there is no available electricity.
In the past, various passive temperature regulation systems have been used in these remote locations to prevent overheating in the warmest parts of the year. In U.S. Pat. No. 4,913,985 such a system is disclosed. This system allows warm water to radiate heat outward into the night sky through a radiator located at an incline on the roof of the enclosure. After the water is cooled in the radiator, it is removed from the bottom of the radiator and circulates through the skin of the enclosure via a pair of conduits. The cooled water is ultimately deposited in the bottom of a water container. Warm water is removed from the top of the water container and transported to the top of the radiator. As warm water enters the higher end of the radiator, the cooling cycle begins again. This system relies on the radiator and conduits to form a thermal siphon at night in order to circulate the warm and cool water between the radiator and the water container.
Although this system ideally reduces the temperature inside of an enclosure, the thermal siphon does not always work in the direction in which it is intended to flow. Subtle atmospheric conditions can cause the cool water from the bottom of the tank to be drawn into the radiator and cold water is returned to the top of the tank. This form of back flow causes the warm water in the radiator and the cold water in the radiator to stagnate, and thus not deliver the cooling effect which is desired.
In U.S. Pat. No. 5,316,872 a system is disclosed by which an enclosed area can be cooled using a quantity of water by a passive apparatus despite the direction in which the thermal siphon is created. By symmetrically aligning the conduits through which the water travels through the skin of the enclosure, the apparatus eliminates any need for a specified thermal siphon direction.
Previously there have been no known passive cooling systems using water which could generate heating and cooling effects in winter and summer respectively using the same plumbing. It was understood that water could be cooled at night by allowing it to radiate heat into the atmosphere. Creating a thermal siphon is a natural and passive way to accomplish this cooling in locations where electricity is not available. It was also understood that exposing water to sunlight causes the water to heat. However, in the past, no known apparatus or method was developed by which this passive cooling of water could be simply combined with pumped heating using the same plumbing.
The present invention provides an apparatus and method by which the temperature of an enclosure can be prevented from reaching extremely high or extremely low points. The enclosure provides a functional area whose temperature is adjusted by heated or cooled water contained within a water container which is located above the functional area and below the ceiling of the enclosure. The water in the water container is heated or cooled, depending on the desired effect, by exposing the water to atmospheric conditions while passing through a radiator/absorber located on the roof of the enclosure. The radiator/absorber has an inclined configuration, with higher and lower ends. The water passes from the water container to the radiator/absorber and back again to the water container through a pair of conduits. A warm water conduit runs between one end of the water container and the higher end of the radiator/absorber, while a cold water conduit runs between the other end of the water container and the lower end of the radiator/absorber. The water will passively travel from the water container to the radiator/absorber during warm weather by creating a thermal siphon at night. A pump is attached to the cold water conduit and used to circulate water in cold weather when heating is desired.
When cooling is desired, and water is circulated between the radiator/absorber and the water container by a naturally creating a thermal siphon, the entire apparatus, including the radiator/absorber, water container, and conduits, must be filled with water. When heating is desired and the pump is required to circulate water throughout the apparatus, the water level is lowered so that when all the water is settled, it just barely fills the water container. Lowering the water level prevents the formation of an accidental thermal siphoning effect at a time when heating and not cooling is desired. As water passes through the radiator/absorber, it either absorbs heat from the sun or radiates heat into the atmosphere. When heating is desired, the water is passed through the radiator/absorber during the day in order to absorb the available solar energy. Cooling is accomplished by allowing the water to thermal siphon through the radiator/absorber at night and radiate the heat absorbed during the day into the atmosphere.
In the preferred embodiments of the present invention, the water container which holds the water above the functional area of the enclosure is composed of a plurality of water tubes. Because the radiant heat and radiant cool must pass through the outer surface of the water container before affecting the ambient temperature in the enclosure, the larger the surface area of the water, the more radiant heat and radiant cool can be exchanged with the functional space of the enclosure. Additionally, the cost of ordinary tubes which are thermally conductive is minimal when compared to the cost of manufacturing a tank to accommodate the various ceiling sizes of different enclosures. In the preferred embodiments, thin wall PVC pipe having an 8 inch diameter, and 0.100 inch thickness work well and cost on the order of $1 per square foot.
In one preferred embodiment of the present invention, the radiator/absorber is a hollow propylene sheet having multiple flow paths from its higher end to its lower end as mounted. Basically, the radiator/absorber in this embodiment of the present invention is very similar to a standard solar collector often used to heat swimming pools, albeit one without flow path inhibitors. In a second embodiment of the present invention, the radiator/absorber preferably has panels which can be rotated from one side to the other. One side of the radiator/absorber panels are preferably covered in flat white paint to discourage the absorption of heat and maximizing heat dissipation when cooling is desired. The other side of the radiator/absorber panels are preferably covered in selective black paint so that solar energy absorption is promoted when heating is desired.
Although the amount of solar energy incident upon the radiator/absorber is less predictable than the regularity with which the darkness of nighttime will appear due to unpredictable weather conditions, heat can be stored in larger quantities than the cooling effect of heat dissipation. As a result of this excess stored heat, the water tubes can cause the temperature in the enclosure to rise above a desirable temperature. In order to prevent the overheating of the functional area of the enclosure, a plurality of adjustable shutters are installed between the water tubes and the functional area of the enclosure in the preferred embodiment. With the shutters completely closed, the radiant heat flux from the water tubes can be reduced from 0.7 BTU/degree Fahrenheit hr. per sq. ft to 0.2 BTU/degree Fahrenheit hr. per sq. ft.
The unitary system and method of the present invention provide both passive cooling and passive heating to an enclosure. All that is required to change the system from heating to cooling is a change in the quantity of the water, and implementation of the pump. During summer, the system and method provide a thermal mass to absorb heat during the day, and dissipate heat during the night, to moderate the temperature within the disclosure. During winter, the pump (which can be solar powered) is actuated to solar heat the water and provide heat to the interior of the enclosure. Shutters can be used to control heat transfer. The system and method thus provide a system for passively heating and cooling the enclosure, and moderating the temperature to provide effective shelter for livestock, and protection from extreme heat for electrical devices. Also, the system and method can be operated in a controlled fashion to provide thermal control for human habitation, particularly if supplemented by more active systems.
The novel features which are characteristic of the invention, as to organization and method of operation, together with further objects and advantages thereof will be better understood from the following description considered in connection with the accompanying drawings in which preferred embodiments of the invention are illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.